1. Field of the Invention
The present invention relates to a laser printer and, more particularly, to a laser printer capable of protecting a photosensitive drum when handling and replacing printer components.
2. Description of the Related Art
Generally, as shown in FIG. 1, a laser printer includes a developing unit 2 and a toner cartridge 3 which are removably mounted on the front of the printer main body 1. The developing unit 2 has a photosensitive drum 2a. When the developing unit 2 is mounted on the printer main body 1, the photosensitive drum 2a is rotatably contacted with a transfer roller 4a. The transfer roller 4a is supported by a side door unit 4 which is mounted on one side of the printer main body 1 to be opened and closed for an easier removal of jammed paper and an easier replacement of the components.
In the above structure, the front surface of the photosensitive drum 2a is evenly charged by an electrostatic charge roller (not shown). An electrostatic latent image is formed on the surface of the charged photosensitive drum 2a by the light scanned from a laser scanning unit 5. Toner is supplied from the toner cartridge 3 and attached on the electrostatic latent image, visualizing the latent image into a preliminary image. A sheet of printing paper is picked up by a pickup unit 7 from a paper cartridge 6, and passed between the transfer roller 4a and the photosensitive drum 2a. While the printing paper is passed between the transfer roller 4a and the photosensitive drum 2a, the preliminary image is transferred on the printing paper. The toner on the printing paper is fixed by a fixing unit 8 while the sheet of paper is passed through a fixing unit 8. After passing the fixing unit 8, the sheet of printing paper is delivered to a stacker via certain routes.
In the meantime, in a printer operated as stated above, for maintenance of the internal components, cleaning, repair, replacement, and so on, the developing unit 2 should be separated from the printer main body 1. For this, a front door (not shown) mounted on the front of the printer main body 1 is opened, thus opening a mounting portion 1a. Then the developing unit 2 is taken out from the mounting portion 1a. If the side door unit 4 is closed, however, since the transfer roller 4a and the photosensitive drum 2a are in a contact with each other, there is a problem in that the photosensitive drum 2a is scratched by the transfer roller 4a while the developing unit 2 is taken out from the mounting portion 1a. This is inconvenient because certain precautionary steps are required of a user when detaching the developing unit 2. Further, the photosensitive drum 2a may be damaged by the carelessness of a user.
Furthermore, in the event that the side door unit 4 is opened, as indicated by the bi-directional arrow ill FIG. 1 while the developing unit 2 is mounted on the printer body 1, the photosensitive drum 2a is exposed through an opened side of the printer main body 1. Accordingly, the life span of the photosensitive drum 2a is shortened since the surface of the photosensitive drum 2a is directly exposed to external light. Accordingly, when opening the side door unit 4, it is desirable to shield the photosensitive drum 2a from external light rays. In addition, the photosensitive drum 2a should not be exposed to the external environment, and it is desirable to prevent the photosensitive drum 2a from being damaged due to a user""s carelessness.
The present invention has been made to solve the above problems, and accordingly, it is an object of the present invention to provide a laser printer having an improved structure capable of preventing an exposure of a photosensitive drum when a side door unit is opened, and also preventing the removal of a developing unit when a side door unit is closed.
The above object is accomplished by a laser printer according to the present invention, including a printer main body having a mounting portion opened by a front door which is mounted on the front side of the printer main body to be opened and closed; a side door unit mounted on a side of the printer main body to be opened and closed, for rotatably supporting a transfer roller; a developing unit removably mounted in the mounting portion when the front door is opened, the developing unit having a photosensitive drum in contact with the transfer roller when mounted in the mounting portion, and an opening for exposing the photosensitive drum to the external environment; an interlock means for preventing the developing unit from being separated from the mounting portion when the side door unit is closed; and a shutter means associated in operation with the interlock means, for closing the opening when the side door unit is opened and opening the opening when the side door unit is closed.
The interlock means includes a sliding member mounted on the printer main body in order to reciprocate between a blocking position in which the sliding member protrudes in an entrance of the mounting portion and a release position in which the sliding member is withdrawn from the entrance of the mounting portion. The, the developing unit may be freely removed from the mounting portion only when the sliding member is withdrawn from the entrance of the mounting portion. The sliding member is moved to the blocking position by being pushed by the side door unit which is coupled to the printer main body. The interlock means also includes a pressing spring for elastically pressing the sliding member to the release position.
The shutter means includes a shutter mounted on an outer side of the developing unit to be moved upward and downward, for selectively opening and closing the opening; a pivoting unit for exposing the opening by moving the shutter downward while pivoted by the side door unit mounted to the printer main body, one end of the pivoting unit being hinged to the shutter, while the other end of the same being hinged to a side of the developing unit; and a pressing spring, for elastically pressing the shutter or the pivoting unit in order for the shutter to close the opening.
A guide member is provided for guiding an upward and a downward movement of the shutter. The guide member includes a guide groove formed around the opening of the developing unit in a generally vertical direction; and a guide protrusion formed on an end of the shutter to slide in the guide groove.
The shutter means includes a pivoting member mounted on the printer main body to reciprocate therein according to the movement of the sliding member, being protruded to an entrance of the mounting portion or withdrawn from the entrance of the mounting portion; a shutter mounted on an outer side of the developing unit to be moved upward and downward, for selectively opening and closing the opening; a pivoting unit for lowering the shutter while being pivoted by the pushing of the pivoting member protruding in the entrance of the mounting portion, one end of the pivoting unit being connected to the shutter, and the other end of the pivoting unit being hinged to a side of the developing unit; and a pressing spring for elastically pressing the shutter or the pivoting unit upward in order for the shutter to close the opening that exposes the photosensitive drum.
The pivoting unit includes a pivoting bracket elastically biased in a direction of pushing the shutter by the pressing spring, one end of the pivoting bracket being pivotably mounted on a side of the developing unit, and the other end of the pivoting bracket having a contact protrusion to be in contact with a pivoting lever; and a connection wire with one end hinged to a side end of the shutter and the other end fixed to the pivoting bracket.
The sliding member includes a slot formed on one end thereof for guiding the movement of the pivoting member, and the pivoting member includes a guide protrusion connected to the slot.